US549477A - Of same place - Google Patents

Description

(No Model!) W. W. DEAN. LOCAL TRANSMITTER CIRCUIT FOR TELEPHCNES.

No. 549,477. Patented Nov. 5, 1895.

' William 1d Dean,

UNITED STATES PATENT OEETCE.

\VILLIAM W. DEAN, OF ST. LOUIS, MISSOURI, ASSIGNOR TO THE BELL TELEPHONE COMPANY OF MISSOURI, OF SAME PLACE.

LOCAL TRANSMITTER-CIRCUIT FOR TELEPHONES.

SPECIFICATION forming part of Letters Patent No. 549,477, dated November 5, 1895.

Application filed March 2 9 1 8 9 5.

vide improved means for producing in a local transmitter-circuit voice-currents adapted to be propagated over a telephone-line to a distant receiver.

In an application for Letters Patent filed February 21, 1895, Serial No. 539,209, I have described a local transmitter-circuit comprising a closed circuit including the microphone and the primary winding of an inductioncoil, the local transmitter-circuit being'con- I nected with the telephone-line at two points, to thus include the local transmitter-circuit in the line-circuit in two parallel branches. Current from a charging-battery connected with the line thus traverses the local circuit in two parallel paths, and the operation of the microphone in one of the paths causes a variation of the current in the two paths of the local circuit. I have also illustrated in said application a form of transmitter-circuit in which the microphone and the primary winding of one induction-coil are included in one of the parallel branches, while the primary winding of a second induction-coil is included in a second branch, the actuation of the microphone thus producing opposite effects in the two induction-coils. The secondary windings of the induction-coils are included in series in the telephone-line, the voltages of the two coils being thus added.

In accordance with the present invention I provide two microphones, one in each of the parallel circuits, the two microphones being connected with a common diaphragm or sounding-board, so that as one microphone increases the resistance through its circuit the other microphone decreases the resistance through its circuit, the two microphones thus acting always in opposite directions.

Serial No. 543,662. (No model.)

The result is to greatly increase the change of current through the two parallel paths. Thus movement of one microphone to increase the resistance of its path causes an increased current through the other path but the microphone in this second path is simul taneously actuated to decrease the resistance through the second path. The current flowing through the second path is thus increased through two causesfirst, the increase of resistance in the first path, and, second, the decrease of the resistance in the second path.

I Will describe my invention more in particular by reference to the accompanying drawings, in which- Figure 1 is a diagrammatic view illustrating my invention. Fig. 2 is a view of the dupleX microphone which I employ in practicing my invention.

Like letters refer to like parts throughout the several figures.

In Fig. 1 I have illustrated a local transmitter-circuit in heavy lines, the circuit comprising two branches a and b; In the branch at is provided a microphone a" and the primary winding a of an induction-coil. In the branch I) is provided a microphone Z) and the primarywindingb of an induction-coil. The secondary windings a and b of the induction-coils are included in series in the telephone-circuit, being connected by conductors c and c with contact points 0 0 against which the switch-hook c rests when the telephone is removed therefrom to close circuit through the limbs (Z (Z of the telephone line, which extends to the central station and terminates in the line-springs d d of a springjack. The line-spring d normally rests upon a contact d, connected through an indicator d and battery e to ground. At the subscribers station is provided a contact f, connected to ground through a bell f. The hook c normally rests upon-contact f to close the circuit of the battery 6 through indicator 61 When the subscriber removes his telephone from its hook, the hook c breaks contact with the contact f, thus opening the circuit of the battery ethrough indicator d whereby the signal for connection is conveyed to the operator, who connects the line of the calling subscriber with the line of the called subscriber by means of plugs g g, inserted in the spring-jacks, as illustrated. In one of the strands of the cord-connectors are provided clearing-out indicators h h, and between the strands is provided abridge 72 containing a retardation-coil 71*, from the center of which extends a. conductor 72" to the 'pole of the battery c.

The receiver 1'. of subscriber A is provided in a bridge between the two conductors c c. The local transmitter-0ircuit of subscriber A is connected to ground at a point I)" and is connected at the point U with conductors c c. The apparatus and connections of substation B are similarto those of sub-station A and have been indicated by corresponding reference-letters. I have illustrated the receiver 'i of substation B asincluded in series with the secondaries of the induction-coils, instead of. in parallel therewith, as shown in sub-station A. The point I) of the local transmitter-circuit at sub-station B is shown connected to ground, while the point 11 is connected to the middle of a retardation-coil 7:, connected in abridge between the conductors c c. I omit further description of the telephone system illustrated, asthis forms no part of the present invention and has been fully described in the application above referred to.

It will be noted that current from battery c passes to the point 11'' of the local transmitter-circuit of sub-station A over the two limbs of the telephone-line in parallel, the current then passing in parallel through the two branches a and b of the localcireuit to ground. As the subscriber at sub-station A talks into his transmitter, the resistance through the microphone to is increased simultaneously with the decrease of resistance through the microphone b. The current flowing through the branch (L is thus decreased, due to the increase of resistance through the microphone a, and, further, to the decrease of resistance through the branch 1). The current through branch Z) is increased, due to the decrease of resistance through the microphone Z) and the increase of resistance through the branch 0. Changes of current-strength are thus produced in the primaries (L2 b of the induction coils,which induce currents in the secondaries (1. 0, the secondaries being wound in such a direction that the voltages of the secondary windings will be added.

In Fig. 2 I have illustrated a form of. transmitter comprising two microphones operated by one diaphragm. Upon the supports I and m are provided carbon buttons l and m, the ends thereof being opposed. Between the opposed faces of the carbons is provided a pin n,carried upon a bracket n,mounted upon the diaphragm 0. As the diaphragm \jibrates the contact between the pin 72. and the carbon buttons Z and m is varied, the pin making more intimate contact with button m and a simultaneously weakened contact with button Z, and vice versa. The contact-pin n and button l may be included in one of the branches of the local transmitter-0ircuit, as the branch (I, while the pin 02. and button m may be included in the other branch 7) of the local circuit.

Having thus described my invention, what I claim as new, and desire to secure by Letters Patent, is

1. The combination with a local transmitter circuit comprising two parallel branches, of two induction coils having their primaries included one in each of the branches of said transmitter circuit and their secondaries in the telephone line, a microphone included in each of the branches of said transmitter circuit and means for simultaneously increasing the resistance through one of the microphones as the resistance through the other microphone is decreased, and a source otcurrent connected with said telephone line adapt ed to direct current through said branches in parallel; substantially as described.

The combination with a local transmitter circuit comprising two parallel branches, of two induction coils having their primaries included one in each of the branches of said transmitter circuit and their secondaries included in series in the telephone line, a microphone included in each of the branches of said transmitter circuit, means for increasing the resistance through one of the microphones simultaneously with a decrease of resistance in the other microphone, and a source of electricity connected with said telephone line adapted to direct current through said branches in parallel; substantially as described.

In witness whereof I hereunto subscribe my name this 25th day of March, A. l). 1895.

'31. \V. DEAN.

\Vitnesses:

EUGENE DEVINE, THos. E. FLAHERTY.

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